So I read through the entire Spriting School thread, and I thought Devamps would be amazing to do. So I stayed up all last night doing a couple because I didn't want to take the course and wait all that time to do my own. What do you guys think of these?

Personally, I did not like this one. The whole skirt was originally green, but that looked odd so I had to use it's actual Gen II sprite for inspiration.

This was the first one I did. It turned out okay.

Eevee's face looks kinda stupid to me, but other than that this one seems fine.

It's been far too long since I've done spriting, so I cannot provide any decent pointers sadly. x3 But I can say that these are looking pretty nice! De-vamps where always my favorite besides re-vamps when it came to spriting. You know, seeing your's here makes me want to try to get back into it actually. Keep up the nice sprites~! ^-^

You do pretty good. When you get really good, you should take the exam.

Anyways... I think that more tethering should be done. It to make it look ore shaded. That could have been done on Bellossom to make the dress different colors. Like dither the green or black into there to make some spots on it darker. You did do good tethering on Deoxys. Another thing that a real 1st gen pokemon (that is what you are aiming for in devamps) is authenticity. And sometimes that includes using a light color as an outline.

On Wartortle the outlines are sometimes the same color it is outlining. And you see on the tail how it made the shell the shading for the white tail. That could be something you take note from. So, all in all, you are doing good! My first ones NEVER looked as good as those. But if you want improvement, here it is.

They look good, but there's some stuff that bothers me.
You're missing some key points in Devamps. Much like plasma said, your sprites have almost no dithering at all. Yes, you're trying to make these sprites look older, but even back then, they still had shading, and that's basically what dithering is: shading.
Another thing you should do is mess with the outlines. I'm sure you were told not to mess with outlines at all, but with Devamps, outlines are something you want to change. The older sprites had spotty outlines, and they often broke off in different places.

With some more practice, I'm sure you can improve. I'd also suggest looking at Devamp tutorials to get some tips from people who're skilled at them.